1. Field of the Invention
The present invention relates to a method for coding an RGB color space signal, and in particular, to a method for coding an RGB color space signal wherein a base plane is encoded using an independent mode, and one or more enhanced plane is encoded by referring to the base plane to reduce a redundancy between RGB planes, thereby improving a compression ratio of an image.
2. Description of the Related Art
Recently standardized H.264/AVC High 4:4:4 profile includes H.264/AVC High 4:4:4 profile COMMON mode and H.264/AVC High 4:4:4 profile INDEPENDENT mode.
The H.264/AVC High 4:4:4 profile COMMON mode is a mode wherein a Cb/Cr signal coding is modified to a Y signal coding in a conventional 4:2:0/4:2:2 format coding of H.264/AVC. That is, contrary to a YCbCr 4:2:0/4:2:2 format coding, a single macroblock has one common Intra/Inter prediction mode and a CodedBlockPattem(CBP) for a Y/Cb/Cr signal, a residual syntax having a format identical to the Y signal is repeated three times. A second and a third residual syntax in the macroblock is for Cb and Cr signals. In other words, the H.264/AVC High 4:4:4 profile COMMON mode is a method wherein an algorithm for coding the conventional Y signal is merely applied to the Cb and Cr signals without adding a new algorithm for coding a 4:4:4 format signal.
The H.264/AVC High 4:4:4 profile INDEPENDENT mode is a method wherein a monochrome coding, which is a conventional 4:0:0/4:2:2 format coding, is applied to each of the Y, Cb and Cr signals independently. Contrary to the COMMON mode, each of the Y, Cb and Cr signals has different macroblock modes and prediction modes in the INDEPENDENT mode. In addition, after a Y plane is coded, a Cb plane is coded, a Cr plane is coded last. The H.264/AVC High 4:4:4 profile INDEPENDENT mode is a method wherein a conventional 4:0:0 format coding algorithm is applied to the Cb and Cr signals without adding a new algorithm for coding a 4:4:4 format signal similar to the COMMON mode.
Contrary to the COMMON mode, because the Y/Cb/Cr signals are independently encoded in the H.264/AVC High 4:4:4 profile INDEPENDENT mode, each macroblock has an independent macroblock mode and intra/inter prediction modes. Therefore, a drawback of the H.264/AVC High 4:4:4 profile INDEPENDENT mode is that a number of bits for representing an information of the macroblock is increased although the H.264/AVC High 4:4:4 profile INDEPENDENT mode is optimal for reducing a residual data. While encoder/decoder may process the Y/Cb/Cr planes in parallel in the H.264/AVC High 4:4:4 profile INDEPENDENT mode, the H.264/AVC High 4:4:4 profile INDEPENDENT mode has a similar to or a slightly lower efficiency than the COMMON mode in view of a compression.
While an algorithm for encoding of an RGB signal in the H.264/AVC High 4:4:4 profile common mode and the H.264/AVC High 4:4:4 profile INDEPENDENT mode is simple because the RGB signal is coded independently, an algorithm for removing a signal redundancy existing in RGB planes is not included. Therefore, an efficiency of the coding is low.
A reason why the algorithm for removing the signal redundancy is not included is that an algorithm of a conventional video coding standard is developed by assuming only an YCbCr color space signal. An YCbCr color space is a color space wherein the signal redundancy of the RGB color space is mostly removed.
Therefore, the encoding of the RGB color space signal is carried out after transforming the RGB color space to the YCbCr color space, and a decoded YCbCr color space is transformed back to the RGB color space to be outputted to a display apparatus.
However, because the inter-transformation of the RGB color space to the YCbCr color space is a lossy transform, a critical problem occurs in a professional environment such as a digital cinema or a medical imaging aiming at a very high fidelity.